Analysis Of Type â…¡ Odontoid Process Fracture Fixed With Anterior Odontoid Screw On A Finite Element Model

Objective To set up the finite element(FE) model of typeâ…¡axis odontoid fracture treated with anterior odontoid screw fixation and analyse the influence of different fixation position of screw different angle of fracture surface to the stability of odontoid process fracture fixed with anterior odontoid screw ,and then find the best biomechanical steady position of anterior odontoid screw.Methods One intact fresh adult cadaveric axis was scaned by CT with 1mm interval. The picture files of CT were transferred to PC and the three-dimensional coordinates were gotten. Those information were utilized to establish the stereoscopic model of axis through the software of PRO/E. The model were transmitted to the program of Ansys, through which material property was yielded. Then it was modifyed and changed to a new model of typeâ…¡axisodontoid fracture fixed with anterior odontoid screw. According to the clinical characteristics of odontoid process fracture, various boundary conditions and loads were endowed. In the condition of different fixation position of screw or different angle of fracture surface, the theoretical stress distribution and displacement of the fracture surface of odontoid process was calculated and compared.Results In the condition of same given outside horizontal force, with the augmentation of the angle between the axis of odontoid process and anterior odontoid screw, the horizontal stress of fracture surface of odontoid process decreased, and that of anterior odontoid screw increased. When a same outside horizontal force was given in the direction of from front to hack, the flexion-type fracture got small displacement and it's surface endured bigger stress than the extension-type fracture, the anterior odontoid screw fixed in flexion-type fracture endured little stress than that in the extension-type fracture. When a same outside horizontal force was given in the direction of from back to front, the results was on the contrary.Conclusion In the condition of same given outside horizontal force, with the decease of the angle between the axis of odontoid process and anterior odontoid screw, the stability of fracture surface of odontoid process increased. Whena same outside horizontal force was given in the direction of from back to front, flexion-type fracture was more unsteady and inclined to displace than extension-type fracture. When a same outside horizontal force was given in the direction of from front to back, extension-type fracture was more unsteady and inclined to displace than flexion-type fracture.